Ink-based digital printing systems, or variable data lithography systems configured for digital lithographic printing, may include an imaging system for laser patterning a layer of dampening fluid applied to an imaging member having a reimageable surface. The resulting latent image is inked to form an ink image for transfer to a printable medium, for example. Such systems are disclosed in U.S. patent application Ser. No. 13/095,714 (“714 Application”), titled “Variable Data Lithography System,” filed on Apr. 27, 2011 by Stowe et al., which is commonly assigned, and the disclosure of which is hereby incorporated by reference herein in its entirety. The 714 Application discloses exemplary systems and methods for providing variable data lithographic and offset lithographic printing or image receiving medium marking.
Methods have been proposed for producing radiation curable inks that are liquid and suitable for ink-based digital printing using variable data lithography systems, such as those disclosed by the 714 Application. U.S. patent application Ser. No. 13/474,185 (“185 Application”), titled “Methods for Manufacturing Curable Inks for Digital Offset Printing Applications and the Inks Made Therefrom,” filed May 17, 2012 by Lee et al. The disclosure of the 185 Application is hereby incorporated by reference herein in its entirety. The 185 Application discloses batch processes for manufacturing improved liquid radiation curable inks that do not gel upon application, have high pigment loading and, optionally, high viscosity as desired.
Inks formulated for ink-based digital printing differ from solid and gel inks. For example, digital offset inks contain a high pigment load—up to ten times higher than solid or gel inks—and therefore have a higher viscosity at room temperature and/or the temperature of application of the ink to the imaging member surface. High shear is required to mix in pigment and to achieve an acceptable pigment particle size. High-shear mixing may, however, cause the ink to gel. This problem, inter alia, is addressed by batch processing for manufacturing liquid radiation curable inks disclosed by the 185 Application, which uses a multi-component system to carry out a multi-step batch process that includes batch mixing and powder dispersion into pigment concentration, three-roll milling, batch mixing of the pigment concentrate into ink, and another step of three-roll milling to produce a batch of radiation curable liquid ink.